Azeotropic distillation of toluene with propionic acid



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uolovulxa AZEOTROPIC DISTILLATION OF TOLUENE WITH PROPIONIC ACID Jan. 13, E948.

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uoivNouovaa xNvl-:NToRs J, w. LATcHuM. JR. BY J. s. CONNOR@ v DHI l Patented jan. 13, 1948 AZEOTROPIC DISTILLATION OF TOLUENE WITH PROPIONIC ACID John W. Latchum,

Bartlesville, Okla., assignors Jr., and James S. Connors,

to Phillips Petroleum Company, a corporation of Delaware Application November 23, 1943, Serial No. 511,492 1 Claim. (Cl. 202-42) This invention relates to the separation of hydrocarbons, and more specifically it relates to the separation of a particular hydrocarbon or type or group of hydrocarbons from hydrocarbon mixtures by means of azeotropic distillation.

In the separation of component hydrocarbons of a crude oil naphtha or of a gasoline, a point is reached after which individual hydrocarbons cannot be separated economically by ordinary fractional distillation. In such distillations, as the temperature rises the number of compounds having boiling points within narrow temperature ranges becomes increasingly great, until beginning in the range of the octanes at about 210 F. the separation of individual hydrocarbons requires reilux ratios so high as to increase the cost of the operation to an inordinate degree. As a result, a number of potentially valuable hydrocarbons are lost in the low grade motor fuel stocks.

Other methods for separating individual or groups of hydrocarbons from petroleum mixtures are known in the art. For example, extraction of aromatics or naphthenics'with selective solvents, as well as adsorption on silica gel or other adsorbents have been employed. Fractional crystallization may be used. None of these methods, however, approach the economy and practicability of distillation in general for the separation of hydrocarbons. Azeotropic distillation has also been used in special cases.

It is also known to eiect the separation of hydrocarbons by means of distillation in the presence of a selective solvent. One example of this latter method involves the use of a polar organic liquid to dissolve selectively naphthenic materials from parafiinic materials in a close cut fraction. The fraction, preferably a 5 F. cut, is fed as a vapor into a column down which.is flowing a stream of selective solvent and liquid reflux. The vaporous material to be extracted (naphthenic material) is dissolved by the selective solvent while the parafflnic material remains as Vapor and passes overhead. The solvent with its dissolved naphthenic materials passes from the contactor into a fractionator wherein solvent and solute are separate, the solute passing overhead as vapor while the solvent is removed as liquid bottoms for recirculation into the original contactor. One important disadvantage in this process is the need for such close fractionation of the feed stock.

On the other hand, according to our invention a feed cut as wide as 30 F., for example, may be used in our azeotropic distillation and with our particular azeotrope former for the isolation of 2 many hydrocarbons. Such materials as toluene or even aromatic mixtures may be separated from hydrocarbon feed stocks in existing fractionating equipment and without the use of excessively high redux ratios.

We have found that paraninic and naphthenic hydrocarbons form azeotropes with a fatty acid. Such azeotropic mixtures possess boiling points below those of the constituent materials and therefore such mixtures pass overhead in a fractionator,

It is an object of this invention toiurnish a method for the separation of toluene from mixtures of toluene and nonaromatic hydrocarbons.

Another object of this invention is to provide a method for the separation of toluene from hydrocarbons mixtures containing toluene and nonaromatic hydrocarbon in a form suihciently pure as to meet product specifications, by the use of conventional fractionating equipment and without the use of excessively high reflux ratios.

Still other objects and advantages will be apparent to those skilled in the art from a careful study of the following disclosure in which The figure represents one form of apparatus, in diagrammatic form. in which the process of our invention may be practiced.

Referring to the figure, numeral 'I refers to a fractionating column, and numerals 2 and 3 to extraction columns. Fractionator I is equipped with an inlet line 4, carrying a side line 20, a bottoms outlet line 5, an overhead vapor outlet line 6, a reflux line 'l and a reboiling heater 8, al1 of which equipment is of conventional design and construction. The vapor outlet line 6 is attached to a condenser 9, which in turn discharges condensate into an accumulator I0. The upper portion of said accumulator is in communication with extraction column 3 by a pipe II in which is disposed an exchanger I5. This latter column is fitted with an overhead outlet line I2, a side inlet line I3, and a bottoms outlet line I4. Extraction column 2 is similar in construction to the extractor 3, and is equipped with an overhead outlet line I6, a side inlet line I'l and a bottoms outlet line I8. Fractionator bottoms line 5 carries a cooling coil I9. Lines I3 and I4 connect with a common line 2I for transfer of bottoms from extractors 2 and 3 to a dehydrator 22, of conventional design. The dehydrator 22 is provided with an outlet pipe 23 for withdrawal of water. A line 24 conducts dehydrated propionic acid to a run storage tank 25. From this storage the acid passes through a pipe 26 to pipe 20 and thence into the hydrocarbon feed line 4. Such minor 3 apparatus and equipment, as valves, pressure regulators, temperature measuring devices, etc., are not shown for reasons of simplicity, the use of such members being well understood by those or run storage tank 2B priorto reuse in the original azeotropic separation step (fractionator I).

The accumulated bottoms in the fractionator I Since the herein disclosed fatty acid is water soluble, Water enters extractor 3 by line I3 to dissolve or extract the said fatty acid from the condensed azeotropes. The thus separated aliphatic hydrocarbons pass from the extractor through line I2 and are conducted to storage, not shown, or otherwise disposed of. The water-propion'ic acid extract phase leaves the bottom of the extractor, since the mixture is'specii'lcally heavier than the hydrocarbons, and passes by way of line 2| to an acid concentrator 22. In this concenvtrator the wash water is removed from the acid, as for example by distillation, leaving a substantially dry liquid propionic acid which may be transferred through pipe 24 tothe intermediate skilled in the art. l 5 are withdrawn through line 5 and pass through 'Ihe operation of the apparatus for the sepacooler I9 into extractor 2 in which water reration of toluene from a hydrocarbon fraction moves any propionic ac1d retainedby the toluene. boiling from about 210 to 240 F., with proponic Water enters the extractor by line Il, toluene acid as the azeotrope former, will be explained. leaves by the overhead line I5 while the water- Referring now to the figure, a hydrocarbon feed l0 propionic acid mixture leaves by line I8 and is stock boiling from about 210 to 240 F. and conadded to the contents of line 2l and passes to the taining toluene enters fractionator I from feed acid conoentrator 22, described hereinbefore. line 4. To this feed stock, just previous to its From the concentrator, substantially dry pro-v entrance into the fractionator, is added the azeopionic acid issues and is passed, preferably to trope former, which is propionic acid. The prothe above mentioned run storage tank 25, pionic acid forms azeotropes with the paraflnic previous to reuse in our system. Separate conand with the naphthenic hydrocarbons, and the centrators may be used if conditions warrant, but amount of fatty acid added is therefore dependit Will generally be desirable to use only a single ent upon the relative amounts of these said concentratorand to pipe the extractor bottoms hydrocarbons in the feed stock. While the com- (water and fatty acid solutions) from extractors position of an azeotropic mixture is constant 2 and 3 to the single unit for removal of the Water under a given set of operating conditions, it is fromthe fatty acid.' well known that the composition varies with pres- The fatty acid ConcentratOr. mentioned obOVe. sure, thus the composition of our azeotropes are may be a distillation unit or other means wheredependent, at least in part, upon the operating by the fatty acid is regenerated in a substantially pressure, Under pressures of 10 t0 30 pounds per v Water free condition, in which condition it is Silitsquare inch, the paraflinic and naphthenic hydroable for reuse. carbons boiling from 210 to 240 F, form azeo- The heating coll 8 in the reboiler section of the tropes with propionic acid containing approxifractionating column may be operated in such a nately propionio acid and about 70% hydro- 30 manner as will give proper separation between carbon The amount of propionic acid added to the aromatic or other bottoms and the lower boilthe feed stock in line 41s in excess of that amount ine azeotropic material, as for example. Ithe required to form the said azeotropes, and the Parafflnand naphthene-DIODiOnC acid azeoexcess, since the fatty acid boils at a temperature trODeS. higher than the boiling range of the hydrocar- The following table ShOWS the Physical Charbon feed stock, will remain in the fractionator acteristics of our proposed azeotrope forming subbottoms. stance, together with suggested boiling ranges of Since the herein disclosed fatty acid forms the hydrocarbon cuts or fractions, the aromatics to type of azeotropes with parafflnic and naphthenic be recovered, and the wash agents to beuused in hydrocarbons having minimum boiling points, 40 recovering the azeotrope former.

Y AromatiA Hsligicsatelgo C Y l' C l' Il Ffid) lvwv. Oirry ZI Ba?" mit tgoggrleggliltgtgggg trope Former F. Propionlc 74 Col.liq .992 284 Water. Toluene... 2l0to240.

jIt is evident that the proposed substance listed y in the above table has the characteristics of a l good azeotrope former, such as: (A), boiling .l

point near the boiling points of the hydrocarbons We have found that the herein disclosed fatty` acid forms the type of azeotropes with hydrocarbons which possesses the minimum boiling points. It hasl also been found that paranic, naphthenic and aromatic hydrocarbons form azeotropes with the disclosed fatty acid, but the minimum boiling mix/tures of these types of hydrocarbons with the fatty acid possesses different boiling points, the paraffin-azeotropes having the lowest boiling points, the naphtheneazeotropes having the next lowest boiling points and the aromatic-azeotropes the highest. In other Words, parainic hydrocarbons have their boiling points lowered most, naphthenie next and aromaties least by use of our azeotrope formers. Thus parafnics or paraflinics and naphthenics may be taken overhead While the naphthenics and aromatics or aromatics alone are the kettle product, depending upon the separation desired. y

This spreading effect on the respective boiling `points then makes it possible to effect the desired separation with a less eiicient column and lower reux ratios, or to attain better separation with existing columns and the usual reflux ratios. The feed should be substantially free from hydrocarbons boiling higher than the aromatic whose separation is desired, though the presence of some hydrocarbons having slightly higher boiling points may be tolerated.

As an illustration of the advantage offered by our invention, the following example is given: A 210240 F. fraction representing approximately of a depentanized natural gasoline, contained 53% parans, 42.5% naphthenes (mostly methyl cyclohexane), and 4.5% toluene. Upon redistillation of this stock in a 'l0-plate column, using a :1 reux ratio and separating the material into three 10 cuts, namely, 210220 F., 220-230 F., and 230-240 F., but without the use of our azeotrope-former, essentially no concentration of toluene (B. P. 231.8 F.) occurred. When this same feed stock was distilled using our propitnic acid azeotrope former in the above mentioned 70-plate fractionator and using the same 20:1 reflux ratio, the paraffins and naphthenes were distilled overhead until the kettle product contained 70-80% toluene.

In some cases the hydrocarbon desired to be isolated may form with the fatty acid such a low boiling azeotrope as to be the overhead product of the fractionator in an exceptionally pure condition, in contrast to the above explained operation. Thus, a parainic material may be separated from a naphthenic and/or aromatic stock as an overhead azeotrope with the herein disclosed azeotrope former. Similarly, a naphthenic hydrocarbon may be separated from aromatics.

'I'he use of the herein disclosed fatty acid is not intended to be limited to the separation of toluene from hydrocarbons mixtures of approximate- 1yequivalentboilingpoints,butmay be used for the separation of naphthenes from paraiins, aromatics from aromatics of diierentdegrees of aromaticity, naphthenes from naphthenes with different numbers of rings, monoand di-olens from aromatics and others. This process applies to natural gasoline fractions, or those from crude oil or cracked or reformed distillates, or to hydrocarbon mixtures having received other treatments. Thus it will be seen that the applicability of our process is wide and that .it is especially useful in the isolation and concentration of many hydrocarbons.

It will be realized by those skilled in the art that many variations and modications of our process and apparatus may be made and yet remain within the intended spirit and scope of our invention.

What we claim is:

A continuous process for the separation of toluene from a hydrocarbon fraction of boiling range up to approximately 30 F. and containing toluene and non-aromatic hydrocarbons comprising continuouslydistilling'said hydrocarbon fraction in the presence of propionic acid wherein the nonaromatic hydrocarbons distil overhead with a portion of said propionic acid as minimum constant boiling mixtures and the toluene containing the remainder of the propionic acid becomes concentrated in the still bottoms; extractingl said propionic acid with water from said overhead constant boiling mixtures leaving a nonaromatic hydrocarbon portion and an aqueous propionic acid extract; extracting the propionic acid with water from said still bottoms leaving toluene and an aqueous propionic acid extract; combining said aqueous propionic acid extracts and substantially dehydrating same and recycling this substantially dried propionic acid into said continuous distillation step, and withdrawing the toluene and nonaromatic hydrocarbon portions as separate products.

J OHN W. LATCHUM, JR. JAMES S. CONNORS.

REFERENCES CITED The following-references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,290,636 Deanesly July 21, 1942 2,360,655 Deanesly Oct. 17, 1944 2,162,963 McKittrick June 20, 1939 2,358,129 Lake Sept. 12, 1944 2,279,780 Engel Apr. 14, 1942 2,380,019 Bloomer July 10, 1945 2,398,689 Bloomer Apr. 16, 1946 OTHER REFERENCES Bureau of Standards Journal of Research; vol. 18, pages 129-134 (Feb. 1937); vol. 21, pages 167-176, 183, 184 (Aug. 1938); vol. 27, pages 39, 40, 44-57, 60-63.

Rossini et al. Proceedings, American Petroleum Institute, sec. III, Refining, Chicago, Ill., Nov. 11-15, 1940, pages 43-47. (Copy in Div. 25.) 202-42-H.

Keyes, Industrial and Engineering Chemistry, vol, 33, pages 1019-1421 (Aug. 1941). (Copy in Sci. Library.) 202-42-H. 

